Pickling of stainless steel



A Patented Sept. 29, 1931 UNITED STATES PATENT OFFICE NATHAN H. SCHERMER, OF YOUNGSTOWN, OHIO PICKLING 0F STAINLESS STEEL No Drawing.

1 solution which usually contains about 50%' hydrochloric acid and about nitricacid, sulphuric acid being sometimes included in addition to these acids.

The use of pickling solutions of this type i is open to many objections, such as their relatively high cost, annoyance and danger to the workmen from poisonous gases and fumes which are expelled from the pickling bath, attack and dissolution of the virgin or base metal resulting in a loss thereof amounting to 3% or 4%, decided pitting or over etching of the surfaces of the metal, lack of uniform- V ity and control of the pickling action, etc.

My invention has for its primary object the elimination of the aforesaid difficulties and disadvantages and the provision of a method of and solutions for cleaning or pickling stainless steel sheets, the use of which 'wilfmateriallylowr the cost of pickling and result in uniform pickling, characterized by the fact that the surfaces of the virgin or base metal are not appreciably attacked or pitted and by the fact that obnoxious and harmful gases and fumes are not expelled from the pickling solutions, thereby avoiding detrimental effects to the workmen.

My pickling solution contains an alkali metal nitrate,=such a sc QQiL m or potassium nitrate in an amount varying from about 2% to" about =-4=0% by weight of thesolutiom ja mineral acid, such as sulphuric-onnitnc.

ac'idand in an amount varying from 2% to about. 40% by*weight--of the solution, and mater-sufficient in amount to make up the bal; 5 anc'eof-the solution. The solution preferably contains about 1% to abou t of gf s odiun pr r e i taamfmtl%.nabestaa signature or llitricacid. The temperature of the pickling bath is preferably ot less than 100? E, but may be nitrate salt'by the action of the sulphuricot Claims:

Application filed August 21, 1930. Serial No. 476,947.

as high as the boiling point of the solution A temperature of about 180 Ffi s fofi fid to be particularly satisfactoi'yi The sheets" of stainless steel are immersed in this bath until the scale is removed or softened to a oint where it may be easily removed by scrub ing.

The cleaning or pickling action of the bath is believed to be dependent upon the liberation of nitric acid in statu nascendi from the nitric acid thereon. This action apparently results in a softening of the scale on the metal which permits it to fall awa from the base metal or to be easily removed by a light scrubbing action.

Since hydrogen is not generated in the pickling bath to an appreciable degree, the pickled sheets are not attacked thereby and are therefore free from hydrogen brittleness.

While I have mentioned sodium and potassium nitrates as salts which may be used in my pickling bath or solution, and sul huric and nitric acids as mineral acids whic may be employed therein, it will be understood that other alkali metal nitrates may be employed as a source of nascent nitric acid and that mineral acids other than sulphuric and nitric acids may be employed to liberate the nascent nitric acid without departing from the spirit of the invention, the scope of which is defined in the appended claims. Moreover, while I have described my invention as par ticularly adapted for the treatment of stainless steel, it will be understood that it may also be effectijif ely'employed for the picklingor cleaning of ordinary iron and steel.

ing the alloys with a solution containing from about 1% to about 5% of a mineral acid and from about 1% to about 5% of an alkali metal nitrate.

4. The method of removing the scale from stainless steel alloys which consists in treating the alloys with a solution containing sulphuric acid and sodium nitrate.

5. The method of removing the scale from stainless steel alloys which consists in treating the alloys with a solution containing from about 2% to about 40% of sulphuric acid and from about 2% to about 40% of sodium nitrate.

6. The method of removing the scale from stainless steel alloys which consists in treating the alloys with a solution containing from about 1% to about 5% of sulphuric acid and from about 1% to about 5% of sodium nitrate.

7. A solution for removing the scale from stainless steel alloys containing a mineral acid and an alkali metal nitrate.

8. A solution for removing the scale from stainless steel alloys containing from about .2% to about 40% of a mineral acid and from about 2% to about 40% of an alkali metal nitrate.

9. A solution for removing the scale from stainless steel alloys containing from about 1% to about 5% of a mineral acid and from about 1% to about 5% of an alkali metal nitrate.

10. A solution for removing the scale from stainless steel alloys containing sulphuric acid and sodium nitrate.

11. A solution for removing the scale from stainless steel alloys containing from about 2% to about 40% of sulphuric acid and from about 2% to about 40% of sodium nitrate.

12. A solution for removing the scale from stainless steel alloys containing from about 1% to about 5% of sulphuric acid and from about 1% to about 5% of sodium nitrate.

In testimony whereof I aflix my signature.

NATHAN H. SCHERMER. 

